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+ Bell Ringer A shopping cart is being accelerated across the floor. What forces are acting on the shopping cart? Draw a diagram representing these forces.

+ Agenda 1. Bell Ringer 2. Balanced vs Unbalanced forces 3. Free body diagrams 4. Free body diagrams stations & practice 5. Exit Slip

+ Learning Targets On your Bell Ringer Sheet, write the following: We will determine when the forces on an object are either balanced or unbalanced.

+ Balanced vs. Unbalanced Forces Balanced Forces Objects DO NOT accelerate Objects remain at constant speed or at rest NET FORCE EQUALS ZERO Ex: Tug of War, no sides winning WHO’S WINNING HERE?

+ Balanced vs Unbalanced Forces Unbalanced Forces Cause objects to accelerate (slow down, speed up, change direction) OR stop Represented by arrows that ARE NOT equal NET FORCE DOES NOT EQUAL ZERO Ex: Tug of War with one side winning WHO’S WINNING HERE?

+ Net Force Net force– sum of all forces acting on an object Forces add and subtract

+ Free Body Diagrams A free-body diagram is a simple diagram that shows the size and direction of all the forces acting on an object

+ Example F Normal F Friction p F Applied F Gravity

+ Steps for Constructing a Free-Body Diagram 1. Draw the object as a box. 2. Draw arrows on the box, each pointing in the direction the force is acting. 3. The size of the arrow represents the size of the force. 4. Label each arrow. F Normal F Applied F Gravity F Friction

+ Copy the table in your notebook SketchFree Body Diagram Balanced or unbalanced? Type of motion

+ Newton’s Laws Practice Quiz handout Answer the questions in your notebook. This is practice for the quiz.

A group of engineers is doing research on how to maximize the efficiency of hybrid cars. They decide to do some test runs first. 1. Draw a free body diagram of the hybrid car before it begins to move. 2. Draw a free body diagram of the hybrid car as it begins to accelerate. Compare and contrast the forces in the free body diagrams above. How do the differences in the forces from the first FBD to the second FBD explain the change in motion of the hybrid car? Answer the questions in your notebooks

+ Question continued…. The engineers decide to modify some components of the hybrid car. 1. On hybrid car A, the engineers made the car bigger and used a stronger, heavier metal. Using Newton’s Second Law, explain why hybrid car A will have a slower acceleration. 2. On hybrid car B, the engineers added a more powerful engine, increasing the force of the car. Using Newton’s Second Law, explain why hybrid car B will have a faster acceleration.

The first FBD shows only gravitational force pushing down and normal force pushing up. Both of these forces are the same and therefore cancel out. There are no forces pushing it along the road. Since there is no net force, and since the forces are balanced, the car does not move and does not accelerate. The second FBD shows an engine force (thrust) that moves the car. There is also frictional force pushing in the opposite direction. Since the car is accelerating, the engine force is bigger than the frictional force. The forces are therefore unbalanced and there is a net force, causing the car to accelerate.

1. The bigger car and heavier metal increase the mass of the car. Since newton’s second law states the F = ma, if the mass of the car increases, and the force stays the same, the acceleration has to decrease. 2. The more powerful engine will increase the force that moves the car. Since Newton’s Second Law states that F = ma, if the force on the car increases, and the mass stays the same, the acceleration has to increase.

+ Calculations with Newton’s Second Law Force = Mass x Acceleration Step 1: Identify the mass Step 2: Identify the acceleration Step 3: Plug it into the equation!

+ Units

+ Practice #1 An object has a mass of 10 kg and accelerates at 5 m/s 2. What is the applied Force?

+ Practice #2 Mike’s car, which weighs 1000kg, is out of gas. Mike is trying to push the car to a gas station, and he can make the car go 0.05 m/s/s (m/s 2 ). What is the force Mike is applying to his car?

+ Draw a cartoon strip In your notebook, draw a cartoon strip of a soccer ball being kicked. For each scene identify if there is a net force and draw a free body diagram. Include the following scenes: Ball at rest The moment it is kicked As the ball flies through the air. The ball rolling on the ground slowing down. The ball at rest again.

+ Exit Slip A book placed on the table and is pushed towards the left with acceleration. Draw a free body diagram. Do not take air resistance into account.